Flooring Deflection On Edge

For example a floor with a span of 10 feet must deflect no more than 1 3 inch or 120 inches 360 inches.

Flooring deflection on edge. Plywood firmly fastened to the undersides of joists helps prevent this side to side bending and stiffens the floor. A taut string stretched across the floor will show the amount of deflection and improvement. Is the live load or the weight of the furniture. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection.

Drywall screws through the plywood and into joists. The l 360 standard means that the floor should not deflect more than the span divided by 360. Of that 10 lb. Typical deflection limits referenced in code books are l 360 l 240 or l 180.

Every floorboard contains both soft spring wood which is the dark grain in each board and dense late season wood. A layer of 3 4 in. Stiffness is measured by the floor s deflection under load. Bedrooms and habitable attic floors l 360 30 psf.

For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. See the table below. Is assumed to be the dead load or the weight of the building materials themselves and 40 lb. Dished out deformities in floorboards are typically caused by poor sanding techniques or by heavy wear in spring wood.

Examples of code prescribed deflection limits and live load values are. As a joist bends downward the lower edge bends slightly to one side or the other. These limits are based on live loads and activities experienced in specific rooms of a house. A common scenario is to install temporary jack posts and support beams then permanent posts and beams over new footings.

The irc says that floors must deflect no more than 1 360 of the floor s span. Span tables and design values. If the span of the joists is 10 feet between supports then the deflection should not be more than 1 3 between the center and the end. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.

The solution to sagging floors or the damaged sills and joist ends that contribute to them often involves jacking. The soft spring wood in this floor was dug out by improper sanding. Divide the total span of the floor joists in inches by 360 to determine the maximum amount the floor can give in the middle under a live load of 40 lb sq. The screws should be no more than 4 in.

Ft plus any long term deflection due to the weight of the floor. Living room floors l 360 40 psf.